(1) Field of the Invention
The present invention relates to a control system of an auxiliary power system for a hybrid electric vehicle. More particularly, it relates to a control system of an auxiliary power system for a hybrid electric vehicle which uses a digital technology, and which the control system monitors a battery charging state and controls an engine at a constant speed.
(2) Description of the Prior Art
Using non-polluting energy sources is becoming more important given the environmental situation where environmental pollution is growing more and more serious. Particularly, the atmospheric pollution of great cities is growing more and more serious, exhaust gas from a vehicle is one of principle factors of atmospheric pollution.
Under this circumstance, electric vehicle is an important solution to overcome the atmospheric pollution. However, the internal effective space of initial electric vehicles is very narrow due to both battery volume and battery weight used in the vehicle body. As a result, vehicle's weight is very heavy. The acceleration time from at rest to a normal speed or to the highest speed is very long. Also, the electric vehicle has a short operating distance and thus the battery needs to be frequently charged. And, the battery charging time is too long in comparison with the time needed to fuel an ordinary vehicle using gasoline.
In order to obviate the shortcomings in travelling performance and with a small displacement in travelling distance, a hybrid electric vehicle with a small displacement internal-combustion engine has been used.
The hybrid electric vehicle is classified as either a serial type or a parallel type according to the energy driving method. The serial type converts the engine's power to electric power through a generator, charges it into a battery, and drives the electric motor with the power charged in the battery. The engine, generator and a driving system are mechanically connected in the parallel type, thus the parallel type charges a margin power into the battery during the engine driving, the engine also providing power to the generator during the vehicle driving by the battery, thereby providing the power to the battery.
Since electric vehicles have not been well accepted in the market place, enhancing the electric vehicle's performance can, result in better acceptance in the market place. Accordingly, even tiny technical improvement in connection with the performance of the electric vehicle is very important.
A major factor to enhance the performance of the vehicle is the battery. Thus, the hybrid electric vehicle performance is based on the battery performance. But, under the same battery, the hybrid electric vehicle performance is based on the auxiliary power system, particularly on a control system of the auxiliary power system.
Under the above background, to effectively control the auxiliary power system, a competition for developing a superior control system is very intensive, and its related technique is growing more and more.
FIG. 1 is a block diagram of a conventional auxiliary power system for a hybrid electric vehicle. As shown in FIG. 1, the conventional auxiliary power system and its control system include: a permanent-magnet generator 10 driven by an engine; a rectifier 20 for rectifying an AC voltage generated from the generator 10 to a DC voltage; a smoothing circuit 30 for eliminating a voltage surge of a rectified DC output waveform; a control circuit 40 for controlling a thyristor gate of the rectifier 20; a current sensing portion 50 for sensing a generated output current; a voltage sensing portion 60 for sensing a generated output voltage; a DC/DC converter 70 for changing a generated voltage to be proper to both the control circuit 40 and a power-supply of each signal processor; a battery 80 which is changed with DC power received from the generator 10 and rectified; a load 90 which is driven by the power applied from the generator 10 and the battery 80; and a contactor 95 which is positioned among the smoothing circuit 30, the battery 80 and the load 90, and switches an electric connection among a power-supply side, the battery 80 and the load 90 according to a command from the control circuit 40 during an abnormal operation of the auxiliary power system.
The voltage sensing portion 60 senses the voltage applied to both the load 90 and the battery 80. If the sensed voltage is lower than a predetermined voltage, the control circuit 40 applies a gate turn-on signal to a control element of the rectifier 20, thus increases a voltage of power transmitted to the load 90. If the sensed voltage is higher than the predetermined voltage, the gate turn-on signal is eliminated, thereby lowering the generated output voltage. The voltage regulation function is performed by repeating the above operations.
The current sensing portion 50 senses the output current of the generator 10. If the generator output current is reached to a limitation value, the control circuit 40 controls a gate turn-on signal, thereby performing a current clamping operation.
If the output of the generator 10 is reached to the overcurrent or overvoltage, the control circuit 40 transmits a turn-off signal to the contactor 95, the power applied to both the battery 80 and the load 90 from the generator 10 is cut off.
A DC/DC converter 70 converts a voltage to another voltage, in order to make the output regulation voltage applied from the generator be proper to the power-supply of the control circuit 40 or each signal processor.
However, since a whole control system of an auxiliary power system for the conventional hybrid electric vehicle is controlled by analog signal, the conventional control system is complicated and its modification is very difficult. Namely, a flexibility of the circuit function is lowered and a circuit protection function is limited.
Further, the control system of a hybrid electric vehicle needs to control the engine at a constant speed, the conventional art shown in FIG. 1 has no function by which the engine is controlled at a constant speed.
Japanese Patent Application (unexamined) Hei 5-168105 relates to the power-supply system of the hybrid electric vehicle.
According to the above Japanese Patent, in a power system of the hybrid electric vehicle which charges a battery with a generated power of the generator driven by an engine and drives a motor at a variable speed by using the generated power and the battery, the power-supply system of the hybrid electric vehicle includes: voltage control means which controls a DC voltage by adjusting a field current; motor control means which controls the motor at a variable speed by using the DC voltage as a power-supply; DC/DC converter which obtains a power-supply from the DC voltage, insulates a voltage detecting signal proportional to the DC voltage, and generates the voltage detecting signal; and current limiting means which restricts an output current to a predetermined current by adjusting the field current.
However, since the power system of the hybrid electric vehicle according to the Japanese Patent Application Hei 5-168105 is controlled by an analog method, the circuit is complicated and its modification for a function addition is very difficult.